The strange moustache sported by a rare Chinese toad was a long-standing evolutionary enigma. Why, scientists wanted to know, did the male Emei moustache toad grow a band of hard spikes on its upper lip in February, only to shed it three weeks later?

On a cold night in 2011, Cameron Hudson stood over a mountain stream in Sichuan trying to answer that question. The University of Guelph graduate student spied two toads locked in combat.

Hudson captured video and sent it to his adviser in Ontario, Jinzhong Fu, a professor of evolutionary biology.

The mystery was solved.

“It was very, very exciting,” says Fu. “We did a little bit of celebrating.”

“It was a proud moment,” says Hudson, if “kind of silly.”

Hudson’s observations confirmed Fu’s hypothesis: the spiky ’stache is used as weaponry by males jockeying for the best nesting sites during their very short mating season. Primo real estate is potentially more attractive to females, and certainly offers an advantage to the eggs the males fertilize and then guard.

The research, published in PLOS ONE this summer, will also fuel debate about a trait shared by Emei moustache toads and humans. Across the animal kingdom, it’s more common for females of a species to be bigger than males. So scientists have long debated why the tendency is sometimes reversed — something seen commonly in mammals and birds, but only in 10 per cent of amphibian species, the Emei moustache toad being one of them.

Hudson’s observations suggest that male toads might be bigger than females for some of the same reasons scientists have hypothesized about mammals.

“I often think of them like amphibian deer,” says Hudson. “At the end of the season their moustaches fall off and they go back into the forest.” (The irony of discussing this work during “Movember” is not lost on Hudson; while some male Homo sapiens grow seasonal moustaches to support men’s health, it often seems like their not-very-ulterior motive is jockeying for attention from mates.)

Emei moustache toads have a very limited habitat. This study focused on just 300 metres of a stream in the Mount Emei UNESCO World Heritage Site in Sichuan. Fu spent several seasons there without seeing the toads use their moustaches, so he decided to send Hudson slightly earlier in February.

The mountain is a popular tourist destination, but Hudson’s job was unpleasant. It involved splashing around a freezing stream at night with a plumbing-inspection camera, trying to catch toads.

Over two seasons he caught 77, microchipping them and taking DNA samples. They’re not very good jumpers, Hudson says, but their keratin moustache spikes do hurt — “like being poked with a pencil.” He also directly observed seven instances of males fighting, often viciously (unlike deer, the toads injure each other; their moustache spikes regrow if broken).

The research produced another puzzle, however. DNA analysis showed that egg clutches were fertilized by multiple males. Given the species’ complicated mating ritual, it’s unclear how that could happen.

Hudson, now a PhD student in Australia studying the invasive cane toad, would love to return one day and find out.